There are many situations in which soil must be compacted in a relatively confined area, as for example when a foundation has been laid for a building and the soil in the area surrounded by the foundation wall needs to be compacted, as a preparation for laying a concrete floor.
A compacting roller machine that is suitable for such a job must be extremely maneuverable, and the drum through which it exerts compacting force should be so arranged in relation to the frame of the machine that the drum can be brought as close as possible to foundation walls and similar obstructions. It will be evident to those familiar with the compacting roller art that the requirements just specified imply a relatively small machine having a relatively short frame and a small turning radius.
In theory it might seem as if some of the relatively large roller machines that have heretofore been developed and marketed would be satisfactory for use in confined areas if they were merely scaled down. Some such rollers have had articulated frames comprising front and rear frame members connected to swing relative to one another about a vertical axis, and usually such a roller had a cylindrical drum at its front and drive wheels at its rear. The articulated connection between the frame members was employed to avoid having either the wheels or the drum arranged to be steerable relative to the frame, thus enabling both the steering mechanism and the propulsion drive to be simplified. A scaled-down version of such a machine would lack the maneuverability needed for operation in confined areas because its articulated frame members could swing only about 40.degree. in each direction, and therefore such a roller would not have a small enough turning radius.
Smaller rollers have been produced that had two drums, one of which was steerable relative to the frame and the other of which was rotatably driven for propulsion of the machine. Such two-drum machines have usually been employed for rolling asphalt paving material or the like. Because the steerable drum could swing to only a limited extent about its vertical steering axis, such a machine--like an articulated-frame roller--had too large a turning radius to be satisfactory for use in confined places. However, even if designed for a small turning radius, such a machine would be unsatisfactory for use on any surface that did not afford good traction to its rotatably driven drum. A roller intended for soil compaction can of course be expected to encounter very uneven and irregular surfaces on which a steel propulsion drum would slip and slide very badly.
Thus the problem of providing a roller machine that is satisfactory for soil compacting in a confined area is actually a compex of problems. The machine must be relatively small, but it must nevertheless be capable of operating on a very irregular surface. It must have a very small turning radius, but the mere provision of a short turning radius does not afford the required maneuverability and controllability if the machine does not have good propulsive traction on irregular surfaces, or if it has a tendency to skid and slide instead of moving in the direction in which it is steered. And of course the desired controllability, maneuverability and traction should not be achieved at the sacrifice of capability for efficient soil compaction.
The conventional cylindrical steel roller drum obviously cannot afford as much traction as a pair of wheels equipped with high-traction tires, but the wheels, to be effective, must both be in contact with the surface at all times, even though the surface is very irregular. If the wheels are to maintain such surface contact, they must be capable of at least limited up and down movement relative to one another and to the frame of the machine, and heretofore it has not been obvious how the wheels could be mounted for such independent up and down movement and still be rotatably driven by an arrangement that was simple and compact enough for a small machine and at the same time sturdy enough for a soil compacting machine. To these difficult requirements must be added the further complication that the wheel drive mechanism should preferably also accommodate steering motions of the wheels relative to the frame, since control is more effective if the wheels are steered rather than the drum.